Magicka Nightblade One-Bar Solo Example - Build PvE - ESO

Craft Alfiq can be subbed out for basically anything that'd provide a good amount of damage or sustain at a decent uptime, other options are BSW, False God, or even Scathing Mage if you want to be cute but probably bad. I'd usually recommend Vengence Leech, but since you want to be using Medusa, you can't justify having to use heavy armor pieces for it. 

If you want to prioritize Group content, use Tzog instead of Medusa (Though that isn't too important, and keep in mind that if you don't have the skill points to level out medium armor, it's probably not worth it), and Bloodthirsty trait on jewels instead of Infused. Infused is better for shorter fights, like trash or solo content. Or even just non-Vet content.

You also won't need a source of Major Breach in group content, as that is something the tank should always bring, even accidently. You'll need less pen too, so Kra'gh should be replaced with Slimecraw.

If you find yourself having any sustain issues, use Incap instead of Soul Harvest as the ultimate.

Use Clockwork Citrus Filet if you are wanting to do your best and don't care about the expensive cost, Witchmother for mellow Solo content, and Ghastly Eye Bowl for group content.

Good luck and have fun in High Isle, Oakensoul Ring is dope <3